Blasting cap



r J. A. HAMMOND BLASTING CAP Filed March 24, 1930 INI/ENTOR.

.TQHN A HAM/wou Feb. 21, 1933 CTI JOHN A. HAMMOND, OF ALBANY, CALIFORNIA, ASSIGNOR TO CALIFORNIA CAP COMPANY, OF OAKLAND, CALIFORNIA, A CORPORATION 0F CALIFORNIA IBLASTING CAP Application led March 24, 1930. Serial No. 438,304.

This invention relates to electrically red blasting caps and has Jfor its object improvements in construction whereby the delay or time of firing after closing the circuit may be more accurately determined, danger of local overheating or premature setting oil of the charge is overcome, a more permanent and easier assembled structure is had, and one which is more waterproof than prior structures of this kind.

In'the drawing accompanying this application the figure is a greatly enlarged longitudinal section of an electrically fired blasting cap of the delay type made in accordance with my invention.

In the figure, 1 is a blasting cap at one end of a time fuse 2 and to the other end of which is secured the inner tubular metal shell 3 of an igniter assembly.

The blasting cap 1 is a metal shell filled with an explosive 4, and is forced longitudinally and tightly over the end of a special fuse 2 which comprises a substantially rigid metal tube, preferably brass, with its bore filled with a` relatively slow burning fuse powder mixture 6 compacted therein.

At the upper end the metal fuse is reduced in diameter to the point 7 and Jforced tightly into the reduced end of the igniter tube 3, while just above the end of the fuse tube 3 is stepped up at 8 to a larger diameter 8 and after a short length again stepped up at 9 to its full diameter.

Spaced outwardly from the inner shell or tube 3 is an outer tubular metal shell 10 reduced at its lower end and formed with a short neck 11 tightly embracing the intermediate portion o tube 3 and extending at its upper end beyond the upper end of the inner shell 3, the proper concentric spacing of the shells being assured by an outwardly directed bead 12 formed on the inner shell.

At a distance spaced about half way down the inner shell is an inwardly directed bead 13 seated against which is an ignition plug 14 of refractory material imbedding insulated circuit wires 15 connected in series with a resistance coil or wire 16 in turn imbedded within an ignition compound 17 fill` ing a cavity at the lower end of the plug 14 thus forming a spitter7 delinitely spaced a relatively great distance from the upper end of the fuse material 6.

Filling the space in outer shell 10 above i the plug 14 is a waterproof compound 18, either a hardened plastic or one which was poured in a molten condition to harden in place. This filling material 18 is prevented by the bead 12 from going into the intershell space 19 and interlocks with an outwardly turned bead 20 in the outer shell so as to form an immovable Waterproof sealing of the upper end of the assembly.

Completing the assembly of tubular metal elements is a metal tube 21 preferably of copper and which is forced tightly at its upper end over the lower portion of the reduced portion 8 of the inner shell, and at its lower end over the outside of the blasting ca shell.

The wall of the tube 3 forming the hollow chamber X between the spitter and upper end of the fuse is perforated with one or more small holes as at 22 near one end of the chamber, while at a point or points adjacent the opposite end of the chamber the wall of the outer shell is perforated 'as at 23 and a wrapping of easily disruptable material 24, such as a thin piece of adhesive rubber tape, is applied around shell 10 to seal the hole or holes 23 principally against the entrance of water when the device is used in Wet places.

Since the assembly as described is hermetically sealed at its upper end and the copper or other relatively soft metal shell 10 and tube 21 are a press fit upon shell 3, and the tube 21 is a press fit over the tubular metal wall of the blasting cap which in turn is a press fit over the rigid metal wall of the fuse element, it will be seen that a unitary rigid waterproof assembly is thus produced in which the parts are all definitely spaced and which may be assembled mechanically with great rapidity and Without variation.

The fuse element being a brass or other rigid walled tube makes it possible to compact the fuse powder within its bore to a definite degree so that each inch of length will have a definite time of burning and so that with assemblies made up with different lengths of the metal fuses in the manner shown the relative delay in firing may be determined with absolute certainty, something not possible with the usual fuse construction consisting of wound layers of textile material or tape which enwrap the powder during the process of manufacture and thus preclude the possibility of endwise compacting the fuse powder to a predetermined degree of compactness.

Besides the above, the rigid metal fuse shell permits of neclring down, as to the point 7, so as to form a positive stop to predetermine the length of chamber X or distance from the upper end of the fuse to the under-end of the spitter or ignition plug 14, a matter of great importance overcoming pre-ignition or entire failure through inability of the gases and heat to properly dissipate.

By the construction using spaced metal shells completely surrounding the chamber X the common danger of burning through the side walls with pre-ignition of the blasting charge in which the assemblage is usually positioned is prevented, and the venting of this chamber at opposite ends at staggered positions as shown provides for a slow escape of the hot gases and distribution of heat so as to avoid any local overheating.

The wrapping of adhesive rubber tissue 24 or any other frail or meltable covering of course gives way at once from the heat and internal pressure developed.

I am perfectly familiar with the manufacture of electrical blasting caps and the difficulties of securing proper joints and definite positions of the elements when crimping the copper shells to the soft walls of the fuse element as heretofore used, the possibility of interrupting the continuity of fuse burning through the crimping operations, also the former attempts at venting the spitter heat through filtering material and upper end of the assembly bringing in other places for leakage and causes of failure, and it is to overcome these former weaknesses that my invention has been perfected and proven perfect after practical testing under almost every known condition of electrical blasting, for it should be understood that in use of a plurality of these caps are simultaneously ignited from a common circuit and that they are of varying delays so as to explode the charges successively one after the other and that the slightest irregularity in their manufacture such as the spacing of the elements within the assemblage, spacing the double walls of the ignition chamber, etc. will destroy the timing, and that by the construction shown herein the delay time of each cap may be accurately predetermined and can always be depended upon, therefore I claim:

1. In a fuse device, a pair of concentrically spaced metal shells, a time fuse and blasting cap at the lower end of the shells, an electric ignition device within the inner shell with lead wires extending out of its upper end, the outer of the shells extending above the inner shell and ignition device and filled above the same with a sealing compound.

2. In a fuse device, a pair of concentrically spaced metal shells, a time fuse and blasting cap at the lower end of the shells, an electric ignition device within the inner shell with lead wires extending out of its upper end, the outer of the shells extending above the inner shell and ignition device and lled above the same with a sealing compound locked in place within the outer shell by a formation thereon.

3. In an electric blasting cap a double tubular body surrounding the igniter formed of spaced shells constricted at one end for engagement one upon the other, and one of the shells rolled with a bead near the other end to hold the shells in concentric spaced relation.

4l. An electric blasting cap comprising a fuse element formed of a rigid metal tube with its bore compacted with the fuse powder, a cylindrical explosive cap longitudinally forced in position over one end of the rigid metal fuse, a tubular metal shell forming an igniter housing forced longitudinally over the opposite end of said rigid fuse, electrical ignition means positioned within said shell, and a metal tube spacedly surrounding said rigid fuse with its opposite ends respectively forced over said explosive cap and the housing shell.

5. An electric blasting cap comprising a fuse element formed of a rigid metal tube with its bore compacted with the fuse powder, a cylindrical explosive cap longitudinally forced in position over one end of the rigid metal fuse, a tubular metal shell forming an igniter housing forced longitudinally over the opposite end of said rigid fuse, electrical ignition means positioned within said shell, a metal tube surrounding said rigid fuse with its opposite ends respectively forced over said explosive cap and an enlargement on the housing shell, and an outer shell concentrically spaced from the housing shell tightly embracing said enlargement and abutting the last mentioned metal tube. 6. An electric blasting cap comprising a fuse element formed of a substantially rigid tube with its bore compacted with the fuse powder, a cylindrical explosive cap longitudinally forced in position over one end of the fuse tube, the opposite end of said fuse tube outwardly reduced to form a shoulder thereon, a tubular shell forming an igniter 1o housing Jforced longitudinally over said opposite end of said fuse tube to abut said shoulder, and electrical ignition means positioned within said shell.

JOHN A. HAMMOND. 

